Options are used to provide extra information to tune or customize the
execution of a program. In case it wasn't clear, options should be
optional. A program should be able to run just fine with no
options whatsoever. (Pick a random program from the Unix or GNU
toolsets. Can it run without any options at all and still make sense?
The only exceptions I can think of are find, tar,
and dd--all of which are mutant oddballs that have been
rightly criticized for their non-standard syntax and confusing
interfaces.)
Lots of people want their programs to have ``required options''.
Think about it. If it's required, then it's not optional! If
there is a piece of information that your program absolutely requires
in order to run successfully, that's what positional arguments are
for. (However, if you insist on adding ``required options'' to your
programs, look in ``Extending Examples''
(section 6.20.5) for two ways of
implementing them with optparse.)
Consider the humble cp utility, for copying files. It
doesn't make much sense to try to copy files without supplying a
destination and at least one source. Hence, cp fails if you
run it with no arguments. However, it has a flexible, useful syntax
that does not rely on options at all:
$ cp SOURCE DEST
$ cp SOURCE ... DEST-DIR
You can get pretty far with just that. Most cp
implementations provide a bunch of options to tweak exactly how the
files are copied: you can preserve mode and modification time, avoid
following symlinks, ask before clobbering existing files, etc. But
none of this distracts from the core mission of cp, which is
to copy one file to another, or N files to another directory.
